The conventional wisdom on certain subjects is so deeply rooted that no amount of evidence disturbs its hold. That's how it is with those dreary predictions that young Americans just won't vote.

Since the late 1960s, the same chorus has been heard from election to election: The young don't care. They're disengaged. They're too wrapped up in their music, their favorite sports and their parties to take an interest in politics. Predicting that the young will vote in large numbers is like saying the Cubs will finally win the World Series.

As it happens, the Cubs are doing well this season, and the evidence is overwhelming that this year the young really will vote in large numbers -- and they just might tip the election.

The trend started four years ago. According to the Center for Information and Research on Civic Learning and Engagement, or Circle, electoral participation among 18- to 24-year-olds increased from 36 percent in 2000 to 47 percent in 2004. For the larger 18-to-29 group, participation rose from 40 to 49 percent.

The 2006 midterm elections brought a greater increase in off-year voting among the under-30s than in any other age group.

Then came this year's primaries: According to Circle, the turnout rate for under-30s nearly doubled between 2000 and 2008, from 9 to 17 percent.

None of this means that young people will vote at the same rate as middle-aged people or senior citizens. The young move around more, and voter registration laws in most states make it harder for the footloose to exercise their rights. It has long been the case that citizens become more involved in politics when they settle down and develop stronger community ties.

Nonetheless, given present trends, it's a near certainty that young people's overall share of the electorate will grow substantially this year.

Defying stereotypes, the young are more engaged in this campaign than are their elders. A Pew Research Center study released this month asked voters whether they considered this year's campaign "interesting" or "dull." Among those 18 to 29, 67 percent called the campaign interesting, as did 66 percent of those 30 to 49. By contrast, 58 percent of those 50 to 64 and 52 percent of those 65 and over saw the campaign as interesting.

The increase in political interest among the young is staggering. Between 2000 and this year, the percentage of those under 30 describing the campaign as interesting was up 36 percentage points; the increase among those 65 and over was a more modest 18 points.

Could the young make a difference in Barack Obama's favor? Again, the answer is clearly yes. Age is one of the most powerful lines of division in this election. In Pew's survey, under-30s gave Obama his largest lead, 56 to 36 percent. He also led among voters ages 30 to 49 but ran behind among voters 65 and over.

This is not a one-time phenomenon. The under-30s were by far John Kerry's best age group in 2004 -- he carried them over George Bush 54 to 45 percent -- and they voted better than 3 to 2 for Democratic House candidates in 2006.

A study released last week by the Rockefeller Foundation and Time magazine helps explain why the under-30s are so engaged and why their political views have more in common with those of the New Deal generation than of the Reagan generation.

Nearly half of the under-30s said that America was a better place to live during the 1990s, the study found, and they think the country will continue to decline. This is a more pessimistic view than that of the older groups. They are also the generation most worried about their own or their families' economic security, and half of them went without health insurance at some point in the past year, more than double the percentage of any other group.

In light of this, it's not surprising that the Rockefeller report found that 86 percent of the under-30s -- significantly more than any other generational group -- said that "more government programs should help those struggling under the current economic conditions."

Young Americans show all the signs of being interested enough and upset enough to flock to the polls this year. If they do, they could be the most politically consequential generation since the cohort of the Great Depression and World War II. Think of these newcomers as the Engaged Generation.